'\" et
.TH PTHREAD_BARRIER_WAIT "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pthread_barrier_wait
\(em synchronize at a barrier
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_barrier_wait(pthread_barrier_t *\fIbarrier\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_barrier_wait\fR()
function shall synchronize participating threads at the barrier
referenced by
.IR barrier .
The calling thread shall block until the required number of
threads have called
\fIpthread_barrier_wait\fR()
specifying the barrier.
.P
When the required number of threads have called
\fIpthread_barrier_wait\fR()
specifying the barrier, the constant PTHREAD_BARRIER_SERIAL_THREAD
shall be returned to one unspecified thread and zero shall be returned
to each of the remaining threads. At this point, the barrier shall be
reset to the state it had as a result of the most recent
\fIpthread_barrier_init\fR()
function that referenced it.
.P
The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in
.IR <pthread.h> 
and its value shall be distinct from any other value returned by
\fIpthread_barrier_wait\fR().
.P
The results are undefined if this function is called with an
uninitialized barrier.
.P
If a signal is delivered to a thread blocked on a barrier, upon return
from the signal handler the thread shall resume waiting at the barrier
if the barrier wait has not completed (that is, if the required number
of threads have not arrived at the barrier during the execution of the
signal handler); otherwise, the thread shall continue as normal from
the completed barrier wait. Until the thread in the signal handler
returns from it, it is unspecified whether other threads may proceed
past the barrier once they have all reached it.
.P
A thread that has blocked on a barrier shall not prevent any unblocked
thread that is eligible to use the same processing resources from
eventually making forward progress in its execution. Eligibility for
processing resources shall be determined by the scheduling policy.
.SH "RETURN VALUE"
Upon successful completion, the
\fIpthread_barrier_wait\fR()
function shall return PTHREAD_BARRIER_SERIAL_THREAD for a single
(arbitrary) thread synchronized at the barrier and zero for each of the
other threads. Otherwise, an error number shall be returned to indicate
the error.
.SH ERRORS
This function shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Applications using this function may be subject to priority inversion,
as discussed in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.291" ", " "Priority Inversion".
.SH RATIONALE
If an implementation detects that the value specified by the
.IR barrier
argument to
\fIpthread_barrier_wait\fR()
does not refer to an initialized barrier object, it is recommended
that the function should fail and report an
.BR [EINVAL] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIpthread_barrier_destroy\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.291" ", " "Priority Inversion",
.IR "Section 4.12" ", " "Memory Synchronization",
.IR "\fB<pthread.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
